The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Rotating fluid machines are used in many applications for many processes. Lubrication for a rotating fluid machine is important. Various types of fluid machines use a thrust bearing that is lubricated by the pumpage. Adequate flow of pumpage should be supplied to obtain proper lubrication. Fluid machines are used under various conditions. During normal operating conditions, lubrication may be relatively easy. However, under various transient conditions, such as start-up conditions, shut-down conditions and during upset conditions, such as passage of air through the machine, lubrication may be lost and therefore damage may occur to the fluid machine. Air entrainment or debris within the pumpage may cause upset conditions.
Referring now to FIG. 1, a hydraulic pressure booster (HPB) 10 is one type of fluid machine. The hydraulic pressure booster 10 is part of an overall processing system 12 that also includes a process chamber 14. Hydraulic pressure boosters may include a pump portion 16 and a turbine portion 18. A common shaft 20 extends between the pump portion 16 and the turbine portion 18. The HPB 10 may be free-running which means that it is solely energized by the turbine and will run at any speed where the equilibrium exists between a turbine output torque and the pump input torque. The rotor or shaft 20 may also be connected to an electric motor to provide a predetermined rotational rate.
The hydraulic pressure booster 10 is used to boost the process feed stream using energy from another process stream which is depressurized through the turbine portion 18.
The pump portion 16 includes a pump impeller 22 disposed within a pump impeller chamber 23. The pump impeller 22 is coupled to the shaft 20. The shaft 20 is supported by a bearing 24. The bearing 24 is supported within a casing 26. Both the pump portion 16 and the turbine portion 18 may share the same casing structure.
The pump portion 16 includes a pump inlet 30 for receiving pumpage and a pump outlet 32 for discharging fluid to the process chamber 14. Both of the pump inlet 30 and the pump outlet 32 are openings within the casing 26.
The turbine portion 18 may include a turbine impeller 40 disposed within a turbine impeller chamber 41. The turbine impeller 40 is rotatably coupled to the shaft 20. The pump impeller 22, the shaft 20 and the turbine impeller 40 rotate together to form a rotor 43. Fluid flow enters the turbine portion 18 through a turbine inlet 42 through the casing 26. Fluid flows out of the turbine portion 40 through a turbine outlet 44 also through the casing 26. The turbine inlet 42 receives high-pressure fluid and the outlet 44 provides fluid at a pressure reduced by the turbine impeller 40.
The impeller 40 is enclosed by an impeller shroud. The impeller shroud includes an inboard impeller shroud 46 and an outboard impeller shroud 48. During operation the pump impeller 22, the shaft 20 and the turbine impeller 44 are forced in the direction of the turbine portion 18. In FIG. 1, this is in the direction of the axial arrow 50. The impeller shroud 48 is forced in the direction of a thrust-bearing 54.
The thrust bearing 54 may be lubricated by pumpage fluid provided from the pump inlet 30 to the thrust bearing 54 through an external tube 56. A gap or layer of lubricating fluid may be disposed between the thrust bearing 54 and outboard impeller shroud which is small and is thus represented by the line 55 therebetween. A filter 58 may be provided within the tube to prevent debris from entering the thrust bearing 54. At start-up, the pressure in the pump portion 56 is greater than the thrust bearing and thus lubricating flow will be provided to the thrust bearing 54. During operation, the pressure within the turbine portion 18 will increase and thus fluid flow to the thrust bearing 54 may be reduced. The thrust bearing 54 may have inadequate lubricating flow during operation. Also, when the filter 58 becomes clogged, flow to the thrust bearing 54 may be interrupted. The thrust bearing 54 generates a force during normal operation in the opposite direction of arrow 50.
Referring now to FIG. 2, another prior art hydraulic pressure booster 10′ is illustrated. The hydraulic pressure booster 10′ includes many of the same components illustrated in FIG. 1 and thus the components of FIG. 2 are labeled the same and are not described further. In this example, the casing 26 has an annular clearance 60 therein adjacent to the thrust bearing 54 and the outboard turbine shroud 48. This provides a small side stream fluid flow to the thrust bearing 54 during startup. The advantage of this process is that the external tube 56 and the filter 58 are eliminated.
Challenges to rotating fluid machines and thrust bearings therein include a high inlet pressure in the pump that may result in a high axial thrust on the rotor in the direction of the turbine 18. Also, during startup pumpage may be forced through the pump portion 16 by an external feed pump upstream of the high pressure booster 10 while the turbine portion 18 runs dry or nearly dry. Flow through the pump impellers may generate a torque creating rotor rotation which may damage the thrust bearing due to the lack of lubrication. Often times, the pressure in the turbine section is much lower than the pump section and thus the lubrication may be insufficient until the full rotor speed is obtained. Process equipment between the pump discharge and the turbine inlet may occasionally introduce air into the turbine. This may occur when the process chamber or system was not purged properly during startup. Consequently, intermittent lubrication to the thrust bearing may be lost.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.